The major cow milk allergen Bos d 5 manipulates T-helper cells depending on its load with siderophore-bound iron

• Published in: PloS one Vol. 9; no. 8; p. e104803
• Main Authors: Roth-Walter, Franziska, Pacios, Luis F, Gomez-Casado, Cristina, Hofstetter, Gerlinde, Roth, Georg A, Singer, Josef, Diaz-Perales, Araceli, Jensen-Jarolim, Erika
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 12.08.2014; Public Library of Science (PLoS)
• Subjects: Allergens; Allergens - immunology; Allergens - metabolism; Animals; Apoptosis; Apoptosis - immunology; Asthma; Biology and Life Sciences; Biotechnology; Catechol; CD4 antigen; Cloning; Coordination compounds; Cow's milk; Data processing; Dissociation; Docking; Flavonoids; Flavonoids - metabolism; Food allergies; Genomics; Helper cells; Humans; Immune response; Immune system; Immunology; Immunomodulation; Immunosuppression; Interleukin 1; Interleukin 13; Iron; Iron - metabolism; Leukocytes (mononuclear); Leukocytes, Mononuclear - immunology; Ligands; Lipocalin; Lipocalins - immunology; Lipocalins - metabolism; Lymphocyte Activation - immunology; Lymphocytes T; Medicine and Health Sciences; Milk; Milk - immunology; Milk Hypersensitivity - immunology; Nutrition; Peripheral blood mononuclear cells; Physical Sciences; Proteins; Quercetin; Siderophores; Siderophores - immunology; Siderophores - metabolism; T-Lymphocytes, Helper-Inducer - immunology; Veterinary medicine; Vitamin A; γ-Interferon; Austria; Germany; Spain
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0104803

The mechanisms of allergic sensitization to milk are still elusive. The major allergen Bos d 5 belongs to the lipocalin-family and thus is able to transport numerous ligands. In this study we investigated its ability to bind to iron-siderophore complexes and tested the immune-modulatory properties of Bos d 5 in either forms. Structural and in silico docking analysis of Bos d 5 revealed that Bos d 5 is able to bind to iron via catechol-based flavonoids (quercetin, myricetin, luteolin) that act as siderophores as confirmed by spectral-analysis and iron staining. Calculated dissociation constants of docking analyses were below 1 µM by virtual addition of iron. When incubated with human peripheral blood mononuclear cells (PBMCs), only the apo-form of Bos d 5 led to an increase of CD4+positive cells and significantly elevated IL13 and IFNγ-levels. In contrast, holo-Bos d 5 decreased numbers of CD4 expressing cells and induced apoptosis. Taken together, our data give evidence that Bos d 5 is capable of binding iron via siderophores. Moreover, our data support for the first time the notion that the form of application (apo- or holo-form) is decisive for the subsequent immune response. The apo-form promotes Th2 cells and inflammation, whereas the holo-form appears to be immunosuppressive.